In the past, strapping is predominantly made of steel and used, for example, to join metal coils, to fasten packaging items to a palette, etc. In practice, plastic strapping is increasingly used in addition to such steel strapping.
Thus, DE 1 099 047 describes a tensioning band with high tensile strength, consisting of a homogenous extruded axially oriented polymeric material. Such plastic strapping offer an advantage compared to steel strapping, because the associated packaging will not be cut and the joining of the ends can be done easily by using, for example, friction welding. However, plastic strapping is not suitable to high temperatures.
Thermal welding is described in DE 40 07 560 [U.S. Pat. No. 5,006,385], among others. Moreover, this document in general deals with the possibility of cutting out individual plastic strapping strips from plastic strapping material. For this purpose, the plastic strapping material is produced as film material, cut into bands and subsequently subjected to stretching to achieve planar alignment of the micro-molecular chains.
In addition, it is of course also possible to produce the plastic strapping directly using extrusion, as described, for example, in WO 2003/087200 [U.S. Pat. No. 7,625,628]. Moreover, plastic strapping is described here that is substantially comprised of polyester and a polyolefin that is not chemically modified.
As a result strapping produced in this manner should have increased resistance to longitudinal splitting. The effect described above nevertheless comes with the disadvantage that the temperature stability of the known plastic strapping has been compromised in certain ways. This can be attributed to the mixture of the main component polyester with polyolefin and for example polypropylene, because the melting point of polyester is about 270° C., whereas the melting point for polypropylene was observed to be 130° C. Thus, the known plastic strapping cannot be used to wrap objects whose temperature is in the previously mentioned range during the strapping procedure. Moreover, there is the further disadvantage with known plastic strapping that the temperature of previously used welding pliers must be adjusted to join the ends in certain circumstances, which reduces acceptance of the relevant band by customers or users.
This fundamental problem also confronts the strapping disclosed in JP 11-245290 A. Actually the strapping in question is produced from raw materials containing up to 60% polyester by weight or more. In addition, elastomers such as for example polyolefin can be added, and at a weighted proportion of from one to twenty parts. Moreover, the further addition of, for example, flame retardants, stabilizers, coloring agents, etc. is mentioned. However, these measures have changed nothing with regard to the lack of temperature stability or the continued inadequate strength for certain uses.
GB 1,132,060 describes plastic strapping that is also concerned with increasing the tensile strength. This indeed applies to extruded film strips, from which then individual strapping strips can be cut out. For this purpose, GB 1,132,060 teaches, for a plastic band with a polyolefin base, the use of 1 to 30% by weight of fibrous material relative to the total mass. In this case, the fibrous material is oriented longitudinally. Such a method thus cannot be used in the production of individual strapping material, because the width of such individual bands is typically 20 to 30 mm with a thickness of up to 1 mm or up to 1.5 mm.
The production of individual strips out of film or filmstrips corresponding to GB 1,132,060 is disadvantageous because the film strips can hardly be produced with a consistently similar material thickness. In addition, there is a concern about inhomogeneities when fibers are added in. It is especially important to keep the material thickness as consistent as possible so that the ends of the plastic bands can be securely attached together. For this purpose, one usually resorts to the previously mentioned welding pliers or welding tongs and hence works with a plastic welding process or a friction welded joint. In both cases, variations in the material thickness of the individual strapping produced cause these not to be connected along the entire surface in the closure area, hence the closure may rupture.